It is known that the harmonic content of input currents of mains-operated electrical equipment is limited by regulations such as EN 61000-3-2. The regulation is valid in a number of countries, and other countries are known to have regulations that restrict a power factor to a minimum level. Nonetheless, there is a need for improving the power factor.
Known ways to improve a power factor include using passive means such as a choke/inductor in series, whereby the choke has a high enough inductance to suppress current harmonics to below the regulation limit. It is also known in the art to use active means to improve the power factor. As regulations become stricter, the active solution is often considered preferable to the passive solution due to the improved effectiveness in improving mains harmonic contents.
The listing or discussion of a prior-published document or any background in this specification should not necessarily be taken as an acknowledgement that the document or background is part of the state of the art or is common general knowledge. One or more aspects/embodiments of the present disclosure may or may not address one or more of the background issues.
According to a first aspect of the invention, there is provided a power conversion controller for controlling the operation of a switch in a power conversion circuit, wherein the power conversion controller is configured to operate the switch according to:
a variable frequency mode of operation for switching frequencies greater than a minimum threshold value; and
a fixed frequency mode of operation at a switching frequency equal to the minimum threshold value.
In this way, an efficient power conversion circuit can be provided that can take advantage of favourable performance of different modes of operation in accordance with how the power conversion circuit is being used. For example, the power conversion circuit can be operated in a mode of operation in accordance with an output power level of the power conversion circuit such that a variable frequency mode of operation is used for low power levels and a fixed frequency mode of operation is used for high power levels.
The fixed frequency mode of operation may be a continuous conduction mode (CCM) of operation. The variable frequency mode of operation may be a boundary conduction mode (BCM) of operation. It has been found that use of a combination of CCM and BCM can provide a particularly effective power conversion circuit.
The power conversion circuit may be a power factor correction circuit.
The power conversion controller may be configured to change from the fixed frequency mode of operation to the variable frequency mode of operation seamlessly when the required output and input powers drop such that a variable frequency mode of operation can be performed at a switching frequency that is in excess of the minimum threshold value.
The power conversion controller may be configured to change from the variable frequency mode of operation to the fixed frequency mode of operation seamlessly when the actual switching frequency in the variable frequency mode of operation (such as BCM) reaches the minimum threshold value for the switching frequency level.
The power conversion controller may be configured to change the mode of operation during a half wave of a signal received at the power conversion circuit. Providing a power conversion controller that can set a mode of operation at a high enough frequency to be able to change the mode of operation during a half wave of a signal (such as a mains signal, or rectified mains signal) received at the power conversion circuit can provide a particularly efficient power conversion circuit.
According to a further aspect of the invention, there is provided a power conversion circuit comprising:
a switch; and
a controller for controlling the operation of a switch, the controller configured to operate the switch according to:                a variable frequency mode of operation for switching frequencies greater than a minimum threshold value; and        a fixed frequency mode of operation at a switching frequency equal to the minimum threshold value.        
The power conversion circuit may comprise a power factor correction circuit. The power factor correction circuit may be a boost converter, a buck converter, a buck-boost converter or any other type of switching-mode power supply (SMPS) circuit. It will be appreciated that embodiments of the invention can be used with any pulse width modulation (PWM) controlled converter. Further examples include Cuk converters, single ended primary inductor (SEPIC) converters, flyback converters, forward converters and half bridge converters.
According to a further aspect of the invention, there is provided a method of controlling the operation of a switch in a power conversion circuit, the method comprising operating the switch according to:
a variable frequency mode of operation for switching frequencies greater than a minimum threshold value; and
a fixed frequency mode of operation at a switching frequency equal to the minimum threshold value.
There may be provided an integrated circuit comprising the control functionality of any power factor correction controller or circuit disclosed herein.
There may be provided a computer program, which when run on a computer, causes the computer to configure any apparatus, including a power conversion controller, circuit, system, or device disclosed herein or perform any method disclosed herein. The computer program may be a software implementation, and the computer may be considered as any appropriate hardware, including a digital signal processor, a microcontroller, and an implementation in read only memory (ROM), erasable programmable read only memory (EPROM) or electronically erasable programmable read only memory (EEPROM), as non-limiting examples. The software may be an assembly program.
The computer program may be provided on a computer readable medium such as a disc or a memory device, or may be embodied as a transient signal. Such a transient signal may be a network download, including an internet download.
A computer program, which when run on a computer, causes the computer to perform any method disclosed herein, or configure any controller disclosed herein, or configure any circuit disclosed herein.